<template>
  <scroll
   class="listview"
   :data="data"
    ref="listView"
   @scroll="scroll"
   :probeType="probeType"
   :listenScroll="listenScroll"
   >
    <ul>
      <li class="list-group" v-for="(group,index) in data" :key="index" ref="listGroup">
        <h2 class="list-group-title">{{group.title}}</h2>
        <ul>
          <li class="list-group-item"
           v-for="(item,index) in group.items"
            :key="index"
            @click="goSingerDetail(item)"
            >
            <img class="avatar" v-lazy="item.avatar" alt="">
            <span class="name">{{item.name}}</span>
          </li>
        </ul>
      </li>
    </ul>
    <div class="list-shortcut">
      <ul>
        <li
        v-for="(item, index) in shortCartList"
        :key="index"
        :class="currentIndex === index ? 'current' : ''"
        @touchstart="onshortTouchstart"
        @touchmove.stop.prevent="onshortTouchmove"
        :data-index="index"
        class="item">
        {{item}}
        </li>
      </ul>
    </div>
    <div class="list-fixed" ref="titleFixed">
      <h1 class="fixed-title">{{fixedTitle}}</h1>
    </div>
    <div class="loading-container" v-show="!data.length">
      <loading></loading>
    </div>
  </scroll>
</template>

<script>
import { getDataAttr } from '@/common/js/dom'
import Scroll from '../scroll/scroll'
import Loading from '../loading/loading'
const ANCHOR_HEIGHT = 18
const TITLE_HEIGHT = 30

export default {
  components: {
    Scroll,
    Loading
  },
  props: {
    data: {
      type: Array,
      default() {
        return []
      }
    }
  },
  data() {
    return {
      scrollY: -1,
      currentIndex: 0,
      diff: -1
    }
  },
  watch: {
    data() {
      setTimeout(() => {
        this._calculateHeight()
      }, 20)
    },
    scrollY(newY) {
      // debugger
      // 左右联动的实现
      const listHeight = this.listHeight
      // 一、在顶部向上拉的时候
      if (newY > 0) {
        this.currentIndex = 0
        return
      }
      // 二、处于中部的位置的时候
      for (let i = 0; i < listHeight.length - 1; i++) {
        let height1 = listHeight[i]
        let height2 = listHeight[i + 1]
        if (-newY >= height1 && -newY < height2) {
          this.currentIndex = i
          // 计算区块上限和滚动Y轴的差值 标题固定在头部
          this.diff = height2 + newY
          console.log(this.currentIndex)
          return
        }
      }
      // 三、在底部 -newY大于height2的时候
      this.currentIndex = listHeight - 2
    },
    diff(newVal) {
      //  向上偏移 有一个顶的效果
      let fixedTop = (newVal > 0 && newVal < TITLE_HEIGHT) ? newVal - TITLE_HEIGHT : 0
      // 减少dom操作
      if (this.fixedTop === fixedTop) {
        return
      }
      this.fixedTop = fixedTop
      // 操作dom 向上偏移
      this.$refs.titleFixed.style.transform = `translate3D(0, ${fixedTop}px, 0)`
    }
  },
  computed: {
    shortCartList() {
      return this.data.map((group) => {
        return group.title.substr(0, 1)
      })
    },
    // 头部标题显示
    fixedTitle() {
      // 先做个判断 不然如果没有underfind 就会报错
      return this.data[this.currentIndex] ? this.data[this.currentIndex].title : ''
    }
  },
  methods: {
    onshortTouchstart(e) {
      let anchorIndex = getDataAttr(e.target, 'index')
      let firstTouch = e.touches[0]
      console.log(e)
      this.touch.y1 = firstTouch.pageY
      this.touch.anchorIndex = anchorIndex
      this._scrollTo(anchorIndex)
    },
    onshortTouchmove(e) {
      let firstTouch = e.touches[0]
      this.touch.y2 = firstTouch.pageY
      let delta = (this.touch.y2 - this.touch.y1) / ANCHOR_HEIGHT | 0
      let anchorIndex = parseInt(this.touch.anchorIndex) + delta
      this._scrollTo(anchorIndex)
    },
    _scrollTo(index) {
      if (!index && index !== 0) {
        return
      }
      console.log(index)
      if (index < 0) {
        index = 0
      } else if (index > this.listHeight.length - 2) {
        index = this.listHeight.length - 2
      }
      this.scrollY = -this.listHeight[index]
      this.$refs.listView.scrollToElement(this.$refs.listGroup[index], 0)
    },
    scroll(pos) {
      // console.log(pos)
      this.scrollY = pos.y
    },
    _calculateHeight() {
      this.listHeight = []
      let height = 0
      this.listHeight.push(height)
      const list = this.$refs.listGroup
      for (let i = 0; i < list.length; i++) {
        let item = list[i]
        height += item.clientHeight
        this.listHeight.push(height)
      }
    },
    goSingerDetail(item) {
      this.$emit('goSingerDetail', item)
    }
  },
  created() {
    this.touch = {}
    this.listenScroll = true
    this.listHeight = []
    this.probeType = 3
  },
  mounted() {}
}
</script>
<style lang="stylus" scoped>
@import '~common/stylus/variable'
.listview
  position: relative
  width: 100%
  height: 100%
  overflow: hidden
  background: $background-color
  .list-group
    padding-bottom: 30px
    .list-group-title
      height: 30px
      line-height: 30px
      padding-left: 20px
      font-size: $font-size-small
      color: $color-text-l
      background: $color-highlight-background
    .list-group-item
      display: flex
      align-items: center
      padding: 20px 0 0 30px
      .avatar
        width: 50px
        height: 50px
        border-radius: 50%
      .name
        margin-left: 20px
        color: $color-text-l
        font-size: $font-size-medium
  .list-shortcut
    position: absolute
    z-index: 30
    right: 0
    top: 50%
    transform: translateY(-50%)
    width: 20px
    padding: 20px 0
    border-radius: 10px
    text-align: center
    background: $color-background-d
    font-family: Helvetica
    .item
      padding: 3px
      line-height: 1
      color: $color-text-l
      font-size: $font-size-small
      &.current
        color: $color-theme
  .list-fixed
    position: absolute
    top: 0
    left: 0
    width: 100%
    .fixed-title
      height: 30px
      line-height: 30px
      padding-left: 20px
      font-size: $font-size-small
      color: $color-text-l
      background: $color-highlight-background
  .loading-container
    position: absolute
    width: 100%
    top: 50%
    transform: translateY(-50%)
</style>